The present invention generally relates to semiconductor devices and more particularly to a semiconductor device having a low-dielectric interlayer insulation film suitable for high-speed operation, and a fabrication process thereof.
In a semiconductor integrated circuit in which a number of active device elements, such as MOS transistors, are integrated on a common substrate, it is practiced to provide a multilayer interconnection structure for electrically interconnecting these active device elements. In a multilayer interconnection structure, a first-layer interconnection pattern is covered by a first-layer interlayer insulation film, and a second-layer interconnection pattern is provided on such a first-layer interlayer insulation film. Further, a second-layer interlayer insulation film covers the second-layer interconnection pattern thus formed on the first-layer interlayer insulation film. Further, there may be a third-layer interconnection pattern and a third-layer interlayer insulation film on the second-layer interlayer insulation film.
When such a multilayer interconnection structure is to be formed in a high-speed semiconductor integrated circuit such as a logic integrated circuit or a high-speed memory integrated circuit, it is desirable to reduce the dielectric constant of the insulation film constituting the interlayer insulation film as low as possible. This demand is particularly acute in the ultrafine semiconductor integrated circuits fabricated according to the design rule of 0.3 xcexcm or stricter. It should be noted that such ultrafine semiconductor integrated circuits generally use four or more layers for the multilayer interconnection structure and the total length of the interconnection patterns therein inevitably becomes a very large value.
When a conventional insulation film such as SiO2, which is formed by a parallel-plate plasma CVD process or by a high-temperature CVD process, or an SOG film which is formed by a spin-coating process, is to be used for the interlayer insulation film in such a multilayer interconnection structure, there arises a problem of increase in the impedance as a result of the electrostatic inductance between the interconnection patterns. It should be noted that such an increase in the impedance leads to the problems of response delay or increase of electrical power consumption.
In view of the shortcomings of the conventional interlayer insulation films, there has been a proposal to deposit a F-doped, low-dielectric SiO2 film by a high-density plasma CVD process. The F-doped SiO2 film thus deposited may be subjected to a chemical mechanical polishing (CMP) process for planarization. In fact, it is possible to reduce the dielectric constant of the interlayer insulation film to 3.4-3.5 by adding F (fluorine) to the SiO2 interlayer insulation film.
FIGS. 1A and 1B show typical examples of conventional multilayer interconnection structure.
Referring to FIG. 1A showing an example multilayer interconnection structure 10A, it can be seen that the multilayer interconnection structure 10A is formed on a substrate 1 in which active device elements such as transistors are formed. The substrate 1 further includes an interlayer insulation film covering the foregoing active devices.
On the substrate 1, there is formed an interconnection pattern 2 of Al or an Al-alloy, and an SiO2 film 3 is formed on the substrate 1 typically by a plasma CVD process so as to cover the interconnection pattern 2 in conformity with the shape thereof. Further, there is formed a planarization film 4 typically of SOG, such that the planarization film 4 covers the SiO2 film 3 with a planarized top surface, and an SiO2 film 5 is formed on the planarization film 4 by a plasma CVD process.
In the example of FIG. 1B showing a multilayer interconnection structure 10B, on the other hand, the interconnection pattern 2 on the substrate 1 is covered by a planarized interlayer insulation film 6 of SiO2 formed by a high-density plasma CVD process, wherein the planarized interlayer insulation film 6 has a planarized top surface. Further, the planarized interlayer insulation film 6 is covered by an SiO2 film 7 formed by a plasma CVD process.
In any of the multilayer interconnection structures 10A and 10B of FIGS. 1A and 1B, the SiO2 film 5 or the SiO2 film 7 is covered by a passivation film of SiN.
In any of the conventional multilayer interconnection structures, the SiO2 film 3, 4 or 6 generally has a dielectric constant of 4.1 or more. Thus, due to the effect of the stray capacitance, the problem of signal transmission delay appears conspicuously when the SiO2 film 3, 4 or 6 is used for the interlayer insulation film of ultra-fine semiconductor devices that are fabricated according to the submicron rules. Further, there arises a difficulty in increasing the clock speed in such ultra-fine semiconductor devices that uses the interlayer insulation film having a dielectric constant of 4.1 or more.
As noted already, it is possible to reduce the dielectric constant of the interlayer insulation film 3, 4 or 6 to the value of 3.4-3.5 by using SiO2 added with F. By using such a F-doped SiO2 film for the interlayer insulation film, it becomes possible to increase the operational speed of the ultra-fine semiconductor devices. However, such a F-doped SiO2 film has a drawback in that the adhesion of the SiO2 film to the interconnection pattern is insufficient and that the F-doped SiO2 film thus formed tends to cause an exfoliation.
Accordingly, it is a general object of the present invention to provide a novel and useful semiconductor device and a fabrication process thereof wherein the foregoing problems are eliminated.
Another and more specific object of the present invention is to provide a semiconductor device having a multilayer interconnection structure using therein a low-dielectric interlayer insulation film of F-doped SiO2, wherein the adhesion of the F-doped SiO2 interlayer insulation film is improved substantially and also the reliability of the semiconductor device.
Another object of the present invention is to provide a semiconductor device, comprising:
a substrate;
a multilayer interconnection structure formed on said substrate;
said multilayer interconnection structure comprising: an interconnection pattern; a F-doped interlayer insulation film covering said interconnection pattern; and a high-refractive index insulation film having a refractive index higher than a refractive index of said F-doped interlayer insulation film, said high-refractive index insulation film being disposed at least one of a top side and a bottom side of said F-doped interlayer insulation film.
Another object of the present invention is to provide a fabrication process of a semiconductor device having a multilayer interconnection structure, comprising the steps of:
covering an interconnection pattern with an interlayer insulation film containing therein F and having a first refractive index; and
forming a high-refractive insulation film on said interlayer insulation film, said high-refractive insulation film having a second refractive index higher than said first refractive index.
According to the present invention, the F ions released from the low-dielectric interlayer insulation film are absorbed by the high-refractive index insulation film that contains an excess amount of Si, by providing the high-refractive index insulation film adjacent to the F-containing, low-dielectric interlayer insulation film. Thereby, the problem of exfoliation of the low-dielectric interlayer insulation film is effectively suppressed.
Other objects and further features of the present invention will become apparent from the detailed description hereinafter when read in conjunction with the attached drawings.